Improving our understanding of demographic monitoring: avian breeding productivity in a tropical dry forest

The ratio of juvenile to adult birds in mist‐net samples is used to monitor avian productivity, but whether it is a “true” estimate of per capita productivity or an index proportional to productivity depends on whether capture probability is not age‐dependent (true estimate) or age difference in capture probability is consistent among years (index). Better understanding of the processes affecting age‐ and year‐specific capture probabilities is needed to advance the application of constant‐effort mist‐netting for monitoring and conservation, particularly in many tropical settings where capture rates are often low. We ranked members of the avian community by capture frequencies, determined if temporary emigration influenced the availability of birds to be captured, and assessed the distribution of birds relative to mist‐nets and the parity between capture‐based productivity estimates and number of fledglings in nest plots in a tropical dry forest in Puerto Rico in 2009 and 2010. Few captures characterized the community of 25 resident species and, when estimable, capture probabilities were low, particularly for juveniles (typically < 0.1). Negative trends in capture probability, temporary emigration, and the distribution of birds suggest that avoidance of mist‐nets influenced capture rates in our study. Increasing mist‐net coverage or moving mist‐nets between sampling periods could increase capture rates. The number of fledglings observed in nest plots (25 ha/plot) did not correlate well with capture‐derived estimates (20 ha/net stations), suggesting the presence of immigrants or failure to find all nests. Our results suggest that indices of breeding productivity from mist‐netting data may track temporal changes in productivity, but such data likely do not reflect “true” productivity in most cases unless age‐specific differences in capture probability are incorporated into estimates. Pilot studies should be conducted to evaluate capture rates and the spatial extent sampled by mist‐nets to improve sampling design and inferences before informing decisions.     

Stress from air emersion fails to alter chloride cell numbers in the gills of rainbow trout

Air emersion stress caused an elevation in blood plasma cortisol of rainbow trout Oncorhynchus mykiss but this acute stressor did not elicit chloride cell proliferation in the gill tissue within 2 weeks following the disturbance.     

Hyalophysa lynni n. sp. (Ciliophora,Apostomatida), a new pathogenic ciliate and causative agent of shrimp black gill in penaeid shrimp

The parasitic ciliate causing shrimp black gill (sBG) infections in penaeid shrimp has been identified. The sBG ciliate has a unique life cycle that includes an encysted divisional stage on the host’s gills. The ciliature of the encysted trophont stage has been determined and is quite similar to that of the closely related apostomes Hyalophysa bradburyae and H. chattoni. Hyalophysa bradburyae is a commensal ciliate associated with freshwater caridean shrimp and crayfish, while H. chattoni is a common commensal found on North American marine decapods. Based on 18S rRNA gene sequence comparisons, the sBG ciliate is more closely related to the marine species H. chattoni than to the freshwater species H. bradburyae. The unique life cycle, morphology, 18S rRNA gene sequence, hosts, location, and pathology of the sBG ciliate distinguish this organism as a new species, Hyalophysa lynni n. sp.     

Anadromous trout threatened by whitefish gill‐net fisheries in the northern Baltic Sea

We estimated the effect of the gill‐net fisheries targeted at whitefish (Coregonus sp.) on anadromous sea trout, Salmo trutta, in the Gulf of Bothnia, Baltic Sea using separate data for fish species. The analysis of sea trout captures was based on tagging and recapture data collected in 1998–2011, while whitefish data were derived from individual samples of commercial fisheries from the same period. The mesh sizes used in gill‐net fishing and the seasonal and temporal distributions of recaptured sea trout and sampled whitefish were compared in the northern and southern Gulf of Bothnia. The trout had typically spent 1–2 years at sea, and they were mainly immature with a median body length of 40–43 cm at the time of recapture in gill nets. Despite the increase in the minimum permitted landing size from 40 to 50 cm in 2008, the median length of recaptured trout remained unchanged during the study period. Most (59%) of the gillnetted trout were caught in the southern Gulf of Bothnia in gill nets with mesh sizes of 40–45 mm, which were also used in the whitefish fishery (72%). In the northern Gulf of Bothnia, nets with a smaller mesh size of 25–39 mm took 83% of the whitefish catch and 39% from recaptured trout. In both areas, the overlap in mesh sizes used to gill‐net catch whitefish and sea trout increased during the study period. There were clear seasonal and areal differences in the relative probability of sea trout being captured in gill nets, suggesting that carefully tailored spatial and temporal restrictions on gill‐net fisheries could provide a tool to protect young sea trout without causing intolerable difficulties for the fisheries targeting other species.     

Respiratory gill surface of the serrasalmid fish, Piaractus mesopotamicus

Gill element dimensions of pacu Piaractus mesopotamicus were estimated and correlated to body mass ( W ), according to the power equation Y=aW^b . The filament number ( b =0.154) and length ( b =0.457) increased with body mass, markedly influencing the respiratory gill surface area ( b =0.769). The high filament number and length, associated with a high secondary lamellae frequency ( a =40.21), are typical of active fish species and may be an adaptation to its migratory movements during reproduction. The comparatively small dimensions of its secondary lamellae are found more commonly in less active species, and may be related to the environmental conditions prevailing in lentic environments, where the species is normally found most of the year. Such features, together with its ability to compensate for oxygen reduction by means of a high ventilatory volume, and the use of aquatic surface respiration (ASR), may account for its adaptative capacity to withstand hypoxic conditions, with a low respiratory energy cost.     

Na+-dependent Ca2+ uptake in isolated opercular epithelium of Fundulus heteroclitus

It is concluded that Ca²⁺ transport across the basolateral membranes of the ionocytes in killifish skin is mediated for the major part by a Na⁺/Ca²⁺-exchange mechanism that is driven by the (transmembrane) Na⁺ gradient established by Na⁺/K⁺-ATPase. The conclusion is based, firstly, on the biochemical evidence for the presence of a Na⁺/Ca²⁺-exchanger next to the Ca²⁺-ATPase in the basolateral membranes of killifish gill cells. Secondly, the transcellular Ca²⁺ uptake measured in an Ussing chamber setup was 85% and 80% reduced in freshwater (FW) and SW (SW) opercular membranes, respectively, as the Na⁺ gradient across the basolateral membrane was directly or indirectly (by ouabain) reduced. Thapsigargin or dibutyryl-cAMP/IBMX in SW opercular membranes reduced Ca²⁺ influx to 46%, comparable to the effects seen in FW membranes [reduction to 56%; Marshall et al. 1995a]. Basal Ca²⁺ influx across the opercular membrane was 48% lower in membranes from fish adapted to SW than in membranes from fish adaptated to FW. Branchial Na⁺/K⁺-ATPase activity was two times higher in SW adapted fish. Accepted: 29 October 1996     

Redescription of Ellobiophrya brevipes (Laird, 1959) N. Comb. (Ciliophora, Peritrichia) and the Fine Structure of its Pellicle and Cinctum

ABSTRACT. A species of peritrich that attaches to gills of the skate, Raja erinacea , was identified by its original describer as a member of Caliperia , a genus characterized by having a noncontractile skeletal rod within the arms of its cinctum and by not having the cinctal arms bonded to one another at their tips. Our observations of the living ciliates confirmed by protargol impregnation and electron microscopy revealed that their cinctal arms are linked by a bouton and that the cytoskeletal structure within them has the fine structure of a myoneme. These characteristics place this peritrich unequivocally in the genus Ellobiophrya and it is thus renamed Ellobiophrya brevipes (Laird, 1959) n. comb. Clumps of epithelial cells clasped by the cincta of E. brevipes show damage at their bases but not on their luminal surfaces. The known species of Ellobiophrya are compared for significant structural differences that separate species of this genus.     

Papyrus swamps, hypoxia, and faunal diversification: variation among populations of Barbus neumayeri

To test whether patches of papyrus swamp contribute to diversification of populations of non-air-breathing fishes, the gill morphology of Barbus neumayeri was compared between a papyrus swamp and several tributaries which differed in oxygen regime. Total gill filament length differed among sites and was negatively related to dissolved oxygen availability, supporting strong selection pressure for low-oxygen tolerance in the swamp interior. Among recaptures of marked B. neumayeri over a 4·5-year period among the focal swamp and connected stream and river sites, 93% of fish were recovered at the site of capture. Some of the individuals that moved crossed physicochemical gradients and traversed long distances within the swamp/stream system. This movement rate would theoretically be sufficient to homogenize gene frequencies among populations. However, randomly amplified polymorphic DNA (RAPD) markers indicated significant genetic differentiation among sites and no relationship between genetic differences and geographical distances among sites suggesting habitat-specific selection pressures on dispersers, rather than insufficient dispersal.     

Hydropsychid (Trichoptera, Hydropsychidae) gill abnormalities as morphological biomarkers of stream pollution

1. The use of morphological gill abnormalities of hydropsychid larvae was assessed in Hydropsyche siltalai larvae exposed to cadmium in the laboratory and Cheumatopsyche lepida and H. pellucidula larvae collected from a polluted river. Two biomarkers were evaluated: (1) Hydropsychid abnormality incidence (HAI), referring to the proportion of individuals with at least some abnormalities, and (2) Hydropsychid gill abnormality indice (HYI), referring to the average number of abnormal gill tufts for all individuals. 2. Abnormality–contaminant relations for both biomarkers were established by studying gill responses along gradients of increasing cadmium and organochlorine concentrations. A cadmium gradient was verified in laboratory exposures, whereas the concentrations of polychlorinated dibenzo‐p‐dioxin (PCDD), dibenzofuran (PCDF) and diphenyl ether (PCDE) of the aquatic moss Fontinalis antipyretica were used as measures of an organochlorine gradient in the field. 3. Morphological abnormalities were easily distinguished as heavy darkening, malformation and/or reduction of single gill tufts. Darkening of the gills appeared to start either at the basal or distal ends. 4. A marked increase of HYI values with increasing Cd concentration reflected a clear abnormality‐contaminant relation, whereas the mere dicotomic classification of larvae as normal or abnormal (HAI) was less informative. High values of both HAI and HYI were associated with high contamination. A significant positive correlation was found between organochlorine concentration in mosses and biomarker values for H. pellucidula, but not for C. lepida. 5. We conclude that HAI indicates deleterious effects, but fails to quantify the severity of degradation. Use of individual gill tufts, as response units in deriving HYI, revealed a simple solution to the quantification problem. Further research into the ecological meaning, physiological background and patterns of gill abnormality is recommended for assessing the applicability and relevance of hydropsychid gill biomarkers.